BROMEC 34 Bulletin of Research on o Metal Conservation
April 2013
Anglophone editor & translator: James Crawford jamesbcrawford76 @ gmail.com Francophone coeditor: Michel Bouchard
[email protected] Francophone translators: Nathalie Richard n.richard.elmesti@ videotron.ca Elodie Guilminot elodie.guilminot @ arcantique.org Marc Voisot horloger @pendulerie.com Hispanophone coeditor: Emilio Cano ecano @ cenim.csic.es Hispanophone translators: Diana Lafuente diana.lafuente@ gmail.com Inmaculada Traver lacirujanadelarte @gmail.com
Editorial This edition highlights innovative European research addressing some common challenges which confront metallic heritage collections. More Mo particularly when options for analysis, conservation conse or restoration of metal-composite metal artefacts are restricted. The abstracts emphasize a range of approaches for ancient and modern metals concerning marine, terrestrial or atmospheric environments. In the light of decreasing funding avenues, the resourcefulness resourcefulness demonstrated by the research abstracts – whether it is financial, organisational or collaborative – is noteworthy. All projects featuring in BROMEC provide funding information; giving potential researchers some ideas of how to source their own financial support. In this edition, research on in situ or post-excavation excavation conservation treatments for iron or copper-alloy ironalloy organic composite archaeological artefacts feature twice. The first is a call for collaboration initiated during a master’s dissertation dissert from France, and the second is a newly launched Greek-French Greek French project. Another French project studies a particular corrosion of bronzes excavated from a river. It highlights the importance of controlling and maintaining relative humidity during conservation conser and museum display. Four innovative projects from Switzerland outline the application of diagnostic, electrochemical and microbiological techniques for material analyses or conservation-restoration conservation restoration treatments. Two of these again focus on problems resulting re from organic-composite composite and/or multi-component multi metal objects. The title image depicts the application of a tool under development: an electrolytic pen for locally removing tarnish from gilt silver. silver Finally a consortium from the Czech Republic is analysing analysing the composition and corrosion of excavated archaeological silver. This will be followed by reproduction of this jewellery by contemporary silversmiths. New details for upcoming conferences are given for: Iron and Steel 2013: Rust, Regeneration and Romance; the 7th International Congress on the Application of Raman Spectroscopy in Art and Archaeology (RAA 2013); the 18th International Conference on Ancient Bronzes; BUMA VIII: International Conference on the Beginning of the Use of Metals and Alloys; Big Stuff 2013; and ICOM-CC’s ICOM Metal 2013. Notably, early (i.e. discounted) registration for Metal 2013 is open until the end of June and accommodation information for the conference in Edinburgh is now online. New announcements include a PhD thesis on the dechlorination of marine archaeological iron (see also BROMEC 29 and 32) and an introduction to the ICOMICOM CC Enamel Working Group. New links for website resources include the American Institute for Conservation (AIC) Metals Conservation Wiki, presentations from Big Stuff 2007, the British Museum’s Library Catalogue, and abstracts from last year’s Bronze Conservation Colloquium. We hope you find this edition informative and enjoyable! James Crawford
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Contents
Calls for collaboration Survey on the stabilization of marine iron-organic composite artefacts...................................................................... 3
New research projects New approaches and applications of electrochemical techniques and corrosion inhibitors for in situ monitoring of shipwrecks and treatment of recovered marine metal-organic composite artefacts ............ 4 MAIA: Microbes for Archaeological Iron Artefacts ....................................................................................................... 5 Fabrication, corrosion and conservation of the silver jewellery from Lumbe’s Garden, Prague Castle ....................... 6
Ongoing research projects The MIFAC-Metal project: a methodology for studying and analyzing microstructures and corrosion profiles of heritage metals; application to metallographic samples from Swiss collections ..................................... 7 CLAMTEC project: development of software for the analysis of historic metals using their Ecorr plots ........................ 8 The St Maurice project: development of an electrolytic pen for cleaning tarnished gilt silverware with wooden cores ................................................................................................................................................ 9
Finalized research projects Conservation of a fluvial deposit of bronzes from Agde-La-Motte............................................................................. 10 Abbreviations and acronyms .............................................................................................................................. 11
General information Future seminars and conferences ......................................................................................................................12 Announcements..................................................................................................................................................13 Websites .............................................................................................................................................................13 National Contacts ...............................................................................................................................................16
Cover image: Local cleaning with an electrolytic pen of the foot of a gilded silver monstrance, St Maurice Abbey Treasure, 1314th c. Picture Atelier de restauration. Abbaye de Saint-Maurice. Refer to abstract by Degrigny, “The St Maurice project: development of an electrolytic pen for cleaning tarnished gilt silverware with wooden cores”. BROMEC website: warwick.ac.uk/bromec BROMEC subscription: warwick.ac.uk/bromec-subscription
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Survey on the stabilization of marine iron-organic composite artefacts 1 (UP1PS)
Call for collaboration
Contact: Virginie Ternisien (virginie.ternisien @ gmail.com) (MAC Lab, UP1PS) Funding: No external funding
In preparation for a PhD, the following work is being performed within a Masters degree by research in heritage conservation-restoration at Université Paris 1 Panthéon Sorbonne. Research focuses on desalination (removal of chlorides) of marine archaeological iron-organic composite artefacts which cannot be separated into their component parts. My dissertation will be based on a literature review as well as on testimonials from conservators dealing with similar artefacts. Based on current research, the use of cathodic polarization in a non-buffered neutral electrolyte appears to be the most favoured method of desalination of composite iron-organic marine artefacts, while maintaining the integrity of the artefact. By testing different stabilization treatments and evaluating their efficiency, my objective is to define the issues to address during my PhD. If you have undertaken desalination of similar composite artefacts, I seek your collaboration by answering the following questions. They are largely inspired by an open letter from Hawley2 to record suggestions made by conservators about the treatment of inseparable composite waterlogged wood-metal artefacts. • Could you provide details of the desalination treatment you applied and their effects on the artefact (organic and iron parts)? • Would you consider the treatment successful? If not, what would you suggest are the reasons for the failure? What were your expectations? What would you have changed in the treatment protocol? • What is your recommended research focus for effective desalination of these kinds of composite artefacts? • What are your thoughts and comments on electrolytic stabilization? • If you know someone who has, or is currently, undertaking similar research, would you be willing to provide their contact information? Thank you for completing the survey, I am happy to share the results with you by email. Your assistance is greatly appreciated to help direct the focus of future research. If you are interested in being a part of this project, please feel free to make contact by email since I am in the process of identifying a suitable research facility where I can undertake the PhD research.
1. Original language version; submitted by author in English. 2. Hawley, J. 1984. WOAM Newsletter March 11.
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New approaches and applications of electrochemical techniques and corrosion inhibitors for in situ monitoring of shipwrecks and treatment of recovered marine metal-organic composite artefacts 1 (TEIA, NTUA, AA) New research project
Contact: Vasilike Argyropoulos (
[email protected]) (TEIA), George Batis (NTUA), Elodie Guilminot (AA) Funding: Archimedes III, January 15 2013 – January 20 2015, € 83 000
This project aims to establish an integrated approach for the in situ maintenance of metal components found on shipwrecks and the treatment of metal-wood composite artefacts when removed from underwater sites for museum display. The work plan involves developing a monitoring program to document in situ the condition of iron and copper alloy elements of shipwrecks. A test rack of coupons of standard composition will be placed near a selected shipwreck and Ecorr and surface pH measurements will be conducted periodically in the Aegean Sea. At the same time Ecorr measurements will be carried out on selected shipwrecks in the Aegean. The intention is to evaluate its effectiveness and usefulness as a condition monitoring tool for the underwater environment of Greece. The developed methods will be tested in situ on modern shipwrecks found off the coast of the island of Paros. The possibility of in situ condition monitoring of the shipwrecks could lead to the development of an integrated preservation plan for shipwrecks using cathodic protection. The research also plans to develop appropriate methods of dechlorination of metals in contact with organic materials (wood, textile, leather) via the application of electrochemical techniques (local electrolysis), followed by the testing of new non-toxic corrosion inhibitors during water removal from the organic parts of the artefact. Local electrolysis will be performed on the metal part using a sponge-like material which contains the electrolyte: ensuring the organic part does not make contact with the alkaline electrolyte. The proposed prototype method is commonly used during monument conservation for dechlorination of steel rods in reinforced concrete, and is yet to be applied to conservation of marine composite artefacts. If successful, this approach would offer a simpler, more cost-effective method to dechlorinate metal parts of composite artefacts. The treatment of the organic part of the artefact would be completed using traditional dewatering and consolidating methods, with the help of the said corrosion inhibitors. The new treatment approach will be tested on composite artefacts raised from the 1868 shipwreck known as Patris, found near the island of Kea. Finally, the project will produce a Good Practice Guide for conservation professionals on the state of the art methods applied to stabilize such artefacts.
1. Original language version; submitted by author in English.
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MAIA: Microbes for Archaeological Iron Artefacts 1 (LAMUN, SNM)
New research project
Contact: Edith Joseph (edith.joseph @ unine.ch) (LAMUN), Daniel Job (LAMUN), Pilar Junier (LAMUN), Marie Wörle (SNM) Funding: Swiss National Science Foundation (SNSF) Ambizione grant PZ00P2_142514/1, 3 years (01.01.2013-31.12.2015)
Archaeological iron artefacts experience serious post-excavation problems when contaminated with salts. Evidence of this ongoing corrosion can be observed in the form of flakes, cracks and finally the loss of shape of an object. Usually, the simplest intervention adopted for the stabilization of archaeological iron artefacts is by immersion in alkaline solutions. This method is based on the slow diffusion of the chloride ions from the objects into the solution. This approach is extremely labour intensive and timeconsuming. Also, there is no direct evaluation that chlorides have been fully extracted; only the extracted soluble chlorides are measured. The aim of this project is to develop and evaluate novel desalination methods. In order to improve extraction of chlorides, we will consider two aspects of a treatment: significantly retarding corrosion, for example by removing oxygen or using alkaline solutions, and increasing the porosity of the corrosion crust by the formation of low molar volume compounds. Here we propose to exploit the unique properties of some microorganisms for the stabilization of archaeological iron. Three different strategies will be adopted; either leading to the formation of stable compounds of low molar volume or using translocation properties. First, we will test some species of fungi that have been reported for their ability to transform metal compounds into metal oxalates, known to be chemically stable compounds of low molar volume. The same approach will be exploited to precipitate magnetite (Fe3O4), another very stable compound of low molar volume. Finally, in order to enhance the removal of chlorides from the iron object, we propose the testing of the possible translocation of chlorides by fungi. Based on the results achieved, we could contribute to the development of a synergetic microbial consortium specially designed for the removal of chloride ions and the simultaneous formation of stable iron compounds. Particular attention will be devoted to the efficiency and impact on metallographic structure of the proposed treatment to overcome the problems associated with the treatments presently in use2. Archaeological iron samples will be also included in the studies in order to validate the new method. This research presents innovative aspects in biogeochemistry of microorganisms and conservation science. A key factor supporting its potential success is the creation of an interdisciplinary research partnership, which brings together experts from the fields of chemistry, microbiology and metal conservation.
1. Original language version; submitted by author in English 2. Scott, D.A., Eggert, G. 2009. Iron and steel in art: corrosion, colorants and conservation. London: Archetype publications Ltd.
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Fabrication, corrosion and conservation of the silver jewellery from Lumbe’s Garden, Prague Castle 1 (IAASCR, ICT)
New research project
Contact: Estelle Ottenwelter (
[email protected]) (IAASCR), Jiří Děd (ICT) Funding: Czech grant agency (project P405/12/2195)
The archaeological collection of silver jewellery (9th century AD) from Lumbe’s Garden necropolis, Prague Castle, is being investigated within the framework of a 3-year project. The conservation-restoration laboratory of the Institute of Archaeology of Prague is collaborating with the Institute of Chemical Technology to identify: 1. materials and manufacturing technologies 2. corrosion mechanisms/typologies 3. suitable post-excavation treatments. To help achieve the first objective the silver jewellery will be characterized to further identify the various methods of manufacture: eg. granulation, filigree, casting, hammering, soldering, fire-gilding. X-radiography and metallographic examination will identify the internal structures, and metalworking methods. Surface and core analyses via scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and X-ray fluorescence (XRF) will be applied to identify the metals, alloys, solders and coatings. Replicas will be produced by a silversmith to test the subsequently proposed hypotheses on the methods of manufacture. Analyses of the replicas will also be performed. Metallographic examinations of fragments will determine morphologies/mechanisms of the corrosion damage (e.g. intergranular).
the
X-ray diffraction (XRD) will provide composition of crystalline corrosion products; allowing their differentiation. Lastly it is intended to highlight evidence of the negative effects of chemical treatment methods which were performed during the last decades (e.g. stripping of corrosion products from the metal core, dissolution of solder and loss of granules). Recommendations of treatments suitable for these kinds of objects, including electrochemical methods (in collaboration with Francoise Urban and Virginia Costa) will be made.
1. Original language version; submitted by author in English.
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The MIFAC-Metal project: a methodology for studying and analyzing microstructures and corrosion profiles of heritage metals: application to metallographic samples from Swiss collections 1 (HEACR, Empa) Ongoing research project
Contact: Christian Degrigny (
[email protected])
(HEACR), Marianne Senn (
[email protected]) (Empa) Funding: HES SO
The conservation and restoration of archaeological and historical metallic artefacts require a thorough understanding of their constituent materials and alterations to limit the risk of new deterioration and to apply remedial treatments which will stabilize corrosion processes, ensure cohesion of the constituent materials and allow the uncovering of the limits of the original surface2 of the object. The invasive and/or destructive nature of metallographic methods and some chemical analyses limit their application to cultural heritage materials. Nevertheless, in the past numerous samples have been taken from metallic archaeological and historical artefacts in Swiss collections and are presently distributed around the diverse institutions of this country. The conclusion from the analyses showed both their great disparity and – for most of them – their specificity. For the MIFAC-Metal project we have reconsidered a representative selection of these samples (32) to combine the examination of their microstructure with the analysis of their corrosion profile. For this we developed a method to describe and analyze the samples; homogenizing the collected information and ensuring their accessibility for conservation-restoration professionals. The selected examination techniques are mainly those which are usually accessible by conservation-restoration laboratories, particularly traditional metallography, scanning electron microscopy combined with energy dispersive X-ray spectroscopy and Raman spectrometry. The results are compiled in digitized files which combine the comprehensive documentation of the initial object and the samples; highlighting the most interesting aspects of the inventoried structures. The copper alloy samples (mainly tin bronzes, with or without lead) date from the 16th century BC to the end of the 18th century AD. Iron alloys, mainly steels ranging from the 3rd-2nd centuries BC to the 20th century AD, are best represented. The corrosion profiles depend naturally on the exposure conditions (atmospheric, burial). The few samples taken from aluminium and zinc alloys are not very oxidized.
1. Translated by M. Voisot and J. Crawford. Original version submitted by author in French; refer to BROMEC 34 French version.
The catalogue of files (in English) may be obtained on request via the contact address below. To facilitate access we plan to put the catalogue online. This educational resource for conservation-restoration professionals will possibly be expanded by new contributions; particularly for historical metals (brasses...) and modern metals (nickel and aluminium alloys...), which are underrepresented in the current catalogue.
2. Bertholon., R., 2000. La limite de la surface d’origine des objets métalliques archéologiques: PhD thèse. Université Paris I Panthéon-Sorbonne.
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CLAMTEC project: development of software for the analysis of historic metals using their Ecorr plots 1 (HEACR)
Ongoing research project
Contact: Christian Degrigny (
[email protected]) (HEACR) Funding: HES SO
CLAMTEC follows on from the 2009 SPAMT-Test project, which was created for technical/scientific object and clock conservator-restorers as a tool for qualitative analysis of composition. Similar in purpose to "spot tests", it aimed to develop a single, simple and low-cost analysis which provides an initial indication of the composition of metal alloy objects under study or conservation2. The working principle of the SPAMT-Test tool is available in BROMEC 30, in which we mentioned the limiting nature of the reference database of 250 Ecorr versus time plots: it was difficult to affirm which plots in the database most closely matched those plots established from samples of unknown composition. The objective of the CLAMTEC project has been to limit this problem through development of a plot comparison software ("DiscoveryMat") based on calculations of the distances which separate them. It also allows the automatic collection of data (per second); making data acquisition more reproducible. The sum of the distances between the 15-minute plots obtained from three solutions (Henniez mineral water, potassium nitrate and sodium sesquicarbonate) applied to the unknown material and to those of a reference material in the database, constitute the cumulative distance (or closeness) used by the algorithm of the software. The references in the database are ordered according to these distances; the most plausible propositions being those which feature the smallest differences. According to their knowledge of the analysed materials (construction technology, colour, use, degradation...) the analyst must then assess the suggestions made by the software. The new CLAMTEC tool consists of: the measurement hardware (comprising a multimeter interfaced for the automatic collection of potentials), the "DiscoveryMat" software, and the SPAMT-Test reference database. It has been tested on a set of representative objects from the Musée International d'Horlogerie (MIH) collection of La Chaux-de-Fonds. Of the 47 tested materials, CLAMTEC was able to propose nearly exact compositions for 44 of them (for brass, brass with lead) or very similar compositions, where the elements are identified, but their concentration was not similar (for quaternary alloys, bronzes with zinc, and maillechorts). These last alloys increased the size of the database to 120 references of differing composition.
1. Translated by M.Voisot, J. Crawford and M. Bouchard. Original version submitted by author in French; refer to BROMEC 34 French version.
DiscoveryMat is a freeware: http://157.26.64.17:8080/bilat-discoveryMatuser/index.html
2. Degrigny C. et al., 2010. Qualitative analysis of historic copper alloy objects by measuring corrosion potential versus time. In Mardikian, P., et al. ICOM-CC Metal WG interim meeting, METAL 10, Proceedings of the International Conference on Metals Conservation. Clemson University, 11-15 October, Charleston.
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The St Maurice project: development of an electrolytic pen for cleaning tarnished gilt silverware with wooden cores 1 (HEACR, ASM) Ongoing research project
Contact: Christian Degrigny (
[email protected]) (HEACR), Denise Witschard (ASM) Funding: HES SO
In 2015 the Saint-Maurice Abbey will celebrate its 1500th anniversary. The treasury of the monastery will be redistributed into a new space and the most remarkable silverware (made of gilt or non-gilt silver, which is atmospherically tarnished) will have its original brilliance returned. Restoration of these exceptional heritage objects present conservators with the delicate problem of cleaning composite artefacts without removing the metal sheets which are nailed onto wooden cores. Mechanical or chemical cleaning techniques are too aggressive in these cases and should be avoided; likewise for traditional electrolytic reduction by immersion. The St Maurice project aims to develop methods for localized cleaning, specifically based on the innovative use of an electrolytic pen. Several undocumented attempts have been made in the past, but they led to undesirable side-effects like staining of the cleaned metal (caused by nonrenewal of the contaminated cleaning solution), or by accidental discharge of the solution onto the wooden core. The tool we would like to develop is inspired by the early work of Arie Pappot (Rijksmuseum, Amsterdam), who developed a pen in which the solution is constantly renewed. For this new pen, we improved the flow of the solution with the addition of two diaphragm pumps: one with a fixed flow for supplying the cleaning solution and the other with a variable flow for its extraction. The positions of the built-in electrodes as well as that of the inflow and outflow tubes may be adjusted. Discharge problems were solved by adding an absorbent pad to the tip of the pen. The first prototype is being tested, with success, at the St Maurice Abbey. Nonetheless, the treatment parameters had to be redefined. The use of the pen, when compared with the immersion treatment, shifts the reduction and oxidation potentials some several hundred millivolts and constant renewal of the solution causes significant fluctuations in current, making it difficult to locate the reduction and oxidation peaks during linear voltammetry. During the second year of the project we will refine the treatment parameters. The ergonomics of the pen will be improved in collaboration with the Laboratoire de Recherches en Anthropotechnologie – EDANA from the Haute Ecole Arc Ingénierie. The new optimized version of the pen will be used for cleaning the most prestigious objects of the treasury.
1. Translated by M. Bouchard and J. Crawford. Original version submitted by author in French; refer to BROMEC 34 French version.
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Conservation of a fluvial deposit of bronzes from Agde-La-Motte (CREAM, AC)
Finalized research project
Contact: Patrick Pliska (ppliska @mairie-vienne.fr) (CREAM), Philippe De Viviès (AC) Funding: No external funding
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In February 2004, a bronze age deposit being threatened by erosion was discovered in the Hérault river (France) during a survey by archaeologists from DRASSM. The deposit was transported within its earthen mass to CREAM in Vienne, where its condition was assessed and it was kept in a humid environment in order to prepare a treatment plan. In demineralised water signs of active corrosion appeared (cracking, surface lifting and unidentified efflorescence) which led to requests for C2RMF to analyse the corrosion products. Much sulphur and oxygen were detected, but no chlorine, as we were expecting. As the water was contributing to deterioration, drying (atmospheres of RH
